Marginal control of gas-filled tubes



Oct. 20, 1936. 1 F, MOREHOUSE ET Al. 2,058,170

MARGINAL CONTROL OF GAS-FILLED TUBES 6nd Structwe u KHSQO www.

Filed Aug. 26, 1932 Grid. PotentL'aZ 4 I i l 4 l A/ Il-ll ATTORN EY Patented Oct. 20, 1'936 Lyman F. Morehouse, Montclair, and Samuel P.

Shackleton, Millburn, N. J., assignors to American Telephone and Telegraph Company, a corporation of New York Application August zc, 1932, serial 10.630584 1 Claim.

This invention relates to electrical circuits and more particularly to circuits employing gas iilled tubes such, for example, as discharge tubes containing a gas such as argon, and also to arrangements whereby the structure and characteristics,

of such tubes may be utilized to obtainmarginal control thereof.

In the past marginal operation has usually been obtained by means of electromagnetic reo lays. I Such practice is limited by the performance limitations of the relays and to the variations encountered in rother portions of the circuit. It has b een necessary to separate the operate margins f or the different steps rather ,widely and ,-15 to design circuits for release values which bear fairly definite ratios to the operate values. cause of these limitations it has not in the past been customary to attempt marginal release features as well as marginal operate features. Even if this were done the ratio of operate to release current required by relays would limit such release values. 'I'he limitations oi the relays, by commercial variations in other parts of the circuits andthe tolerances required for maintenance were all such as to greatly restrict the number of independent margins which could be obtained.- 'Ihe objects of the invention and the methods of attaining themwill appear more fully from the detailed description thereto hereinafter 3o given.

It is one of the purposes of the invention to utilize the characteristics of gas fille-.l tubes as determined by any or all of the various factors affecting the characteristics and to use the tubes and associated circuits for the control o! margins, both for operation and for release and for combinations oi operation and release. Such use may be made applicable to signaling or switching circuits or systems or to any uses where marginal o control of circuits may be desired.

The invention may be more fully understood from the following description together with the accompanying drawing in the Figures 1, 2A, 2B

and 3 of which the invention is illustrated. Figs.

5 1, 2A and 2B are graphical illustrations of certain principles of operation c! the arrangements. Fig.

3 is a circuit diagram embodying one form of the invention.

CertainA gas lled tubes have characteristics 50 such as those shown in Fig. 1 in which Ip represents the discharge or anode current for one particular .tube and for one set of Y conditions.

For these conditions it is assumed that the cathode current and anode voltage are kept constant 55 and that the grid potential is varied from a value represented by -Eio to a value E10 and back to -E1o. At a point I ,Y which point is determined by the structure ofthe tube elements, by the gas in the tube, by the temperature-of the cathode and by the value of potential impressed on the 6 anode of the tube, ionization of the gas takes place and an arc is set up between the cathode and the anode. The magnitude of the arc or discharge current is represented by the line Ip and for all values of grid potential which are more positive l than that atpoint I this value prevails. It also prevails upon lowering the grid potential to values negative to point I until a point 2 is reached at which positive ions are eliminated from the region between-grid and cathode being all drawn l to the grid. This reestablishes aregion of negative potential gradient away from the cathode `from which electrons can no longer escape. Ionization of the gas between cathode and. anode ceases and the arc is extinguished. Thence until the value of grid potential -Em is reached or for any values between E1n and point I no current will ow between cathode and anode.

If now conditions are kept the same for-the same tube, except that a diierent value of anode breakdown may be obtained between -Eio and 0 or even for positive values of grid potential.

'Similarly the grid potential at which the arc is 35 extinguished, which may be termed the quenching point, may also be controlled. An illustration of a gas-filled tube having-characteristics such as those shownin Fig. 1 will be found in l U. S. Patent No. 1,944,888, to H. H. Haglund, o issued January 30, 1934.

The gas filled tube may be controlled in a marginal manner, as will be hereinafter pointed out, by varying other of their characteristics; `for example, the gaseous content might be mercury` vapor in which a-.discharge may be started at about' 10 volts effective potential, while if the gaseous content were helium this would be increased to 20 volts. Thus by employing mercury and helium tubes in conjunction in a circuit marginal control could be eilected, as a voltage whichv would sustain an arc in mercury vapor would be insumcient in helium. Another method of obtaining marginal control would be by varying the design of' the tube elements; for example, the 55 use of a grid having a fine mesh would result in a large control ratio, while a grid of coarse mesh would result in a low control ratio.

This latter eect may be illustrated by Figs. 2A and 2B which give an example of the eEect of change in grid structure. In the upper portion of Fig. 2A is shown a set of curves illustrating the potential gradients which might exist lfrom cathode to anode of a gas filled tube with a fairly open grid structure, such as the grid structure |00. The negative grid potential is shown as Eg. The lower of the light lines indicates the potential gradient via the grid structure itself. The other lines indicate the potential gradients, through the open sections of the grid, The heavy line, indicates the average potential gradient. From the heavyand light lines, it will be seen that the potential gradient away from the cathode is negative and accordingly, the electrons cannot iiow from the cathode to anode.r Under such conditions the tube will not discharge. In the lower portion of Fig. 2A is shown a similar set of curves illustrating the potential gradients of the same tube with grid structure IIJIl under similar conditions except that the grid potential is changed to a value Eg. It will be noted that E'g is algebraically greater than Eg. Under this changed condition of grid potential E'g, it will be seen that some of the potential gradient lines from cathode to anode will have a positive slope away from the cathode. Accordingly, electrons may flow from cathode to anode and a discharge will be started in the tube. In other words with a grid structure such as |00 it may be possible to cause the tube to discharge by changing the grid potential" from a value Eg to Eg. In'Fig. 2B are shown sets'of curves illustrating the potential gradients between cathode and anode of a discharge tube having a solid grid structure perforated by very small holes. such as grid structure IUI. In the upper portion of Fig. 2B the same cathode, anode, and rgrid potentials are used as in the case illustrated in the upper portion of Fig. 2A. In the lower portion of Fig. 2B the same cathode, anode and grid potentials are used as in the case illustrated in the lower portion of Fig. 2A. It will be seen that the average potential gradient away from the cathode as shown in the upper portion of Fig. 2B, with a grid potential'of Eg will be negative. It will also be seen from the curves in the lower portion of Fig. 2B that, when the grid potential is changed to E'g, the potential gradient away from the cathode will also be negative. Accordingly, a change of grid potential from Eg to E'g will not operate a tube with a grid structure .such as IIltl. Thus it will be seen that by using tubes with diierent grid structures marginal control or operation thereof may be effected. s

In Fig. 3 the gas filled tubes V1, Va, Vs and V@ are provided to give marginal steps for control of secondary circuit operations as .represented by relays S1, S2, S3 and S4 respectively. In the arrangements of Fig. 3 the marginal control of the tubes is effected by providing the tubes with different xed anode potentials and by applying different potentials tothe grids thereof. Each of the relays S1, S2, Sa and S1, is connected from a source of anode potential Be to the anode of. the tube corresponding to its marginal step. B6 is shown as a common source of anode potential for all of the tubes and to give the desired difference in anode voltage a potentiometer device consisting of resistances R11, R12, R11, R14 and R15 is used for the supply to the several tubes. Separate sources of different values of IIl, and resistance Rs to a battery. B5.

lsistance R5, to battery Bs.

aosaivo plate potential could be used if desired. With the arrangements shown it will be seen that the tube V1 will have the highest anode potential. The anode potential for tube Va will be lower than that of V1. The anode potentials of tubes Va and V4 will in turn be lower than those of preceding tubes. The tubes all receive a negative grid potential from the common source Bs of such a value as to -keep them from discharging. Current limiting resistances R1', Rz', R3' and R1' are provided in the individual grid circuits.

For convenience the tubes are of the so-called heater type with the cathode insulated from its heatersupply. This is not necessary but is a convenience in separating working parts of the circuit from the source of cathode energy.

The control for the various marginal steps is obtained over conductor I 0, which in practice may be a conductor between two oiiices or between two parts of an office interconnected by means of switches or otherwise. The control of the individual steps is lodged with relay or other switch contacts II, I2, I3 and Iii which( close a circuit from battery B5, through resistance 5, conductor I0 and one or more of resistances R1, R2, Ra and R4.

In practice, if it is desired to operate marginal step S1 but not the others, relay contact II is operated. This will connect ground through resistances R1, R2, Ra and R4, over conductor This will reduce the negative potential provided for the grids of al1 the tubes by battery B5 to such a value as to cause ionization in tube V1 above. This is because tube V1, as heretofore pointed out, has the highest anode potential of all the tubes. The anode potentials of the other tubes are suflciently lower than that of V1 so that the reduction of negative grid potential caused by operation of contact II will not be sufficient to cause ionization to take place therein at this time. Ionization of tube V1 permits current to ow from battery Be, through resistance R11, winding of relay S1, anode-cathode path of tube V1, to ground. This will cause the relay S1 to operate. It may control a work circuit not shown.

To operate relay S2 the relay contact I2 will be closed. This will connect groundy through resistances R2, R3 and R4, over conductor IG, re-

This Will further reduce the negative potential applied from B5 to the grids of the tubes to such a point that ionization will take place in tube V2. As heretofore pointedout the anode potential of tube V2 is less than that of V1. Hence to cause ionization in V2 the negative grid potential has to be reduced further than in the case of tub/c` V1. The ionization of tube V2 will permit current to flow from battery Be, through resistances R11 and R11, winding of relay S2, anode-cathode path of tube Vn, to ground. This will operate relay S2, which may control a work circuit not shown. The operation of relay S2 will open at its upper contact the plate circuit of tube V1 and thus deenergize tube V1. v

In a similar manner the operation of switches I3 and It willfurther reduce the negative potential applied to the grids of the tubes and will cause the operation of tubes Va and V1. It is pointed out that when Sa operates it will open the plate circuit of tube V2 and thus deenergize s tube V1. The deenergization of tube V2 will cause the release of relay S2. This will again close the plate circuit of tube V1 -and as the voltage on the grid of tube V1 is below the value needed to 75 break down this tube it will again be operated. In a similar manner the operation of S4 will release Sa, and the release of S3 will allow tube V2 to again become energized.

It has been shown how the arrangements of Fig. 3 permit marginal or selective operation of the gas filled tubes V1, V2, V3 and V4. In a like manner it is possible to secure a marginal or selective release of these tubes. This may be accomplished in the following manner: As heretofore pointed out the release of switch I4 increases the amount of negative potential applied to the grids of the tubes V1, VzfVa and V4. It has also been pointed out previously that tube V4 has the lowest anode potential applied thereto and that progressively greater anode potentials are applied to tubes V3, Va and V1 respectively. Referring to Fig. 1, the characteristic designated Ip illustratesthe variation in anode current when the grid potential is varied. lI'he arc is started,

as indicated by the vertical line rising from I, and the quenching of the arc is shown by the vertical line from Ip to 2. It will be observed that the starting and quenching potentials are close together due to the'low anode voltage. It will, therefore, be possible to so adjust resistances R1, R2, R3, R4 and R5 that the release of switch I4 `will make the grid of tube V4 sufciently negative to quench the arc therein. `When this occurs relay Si will release completing the anode circuit of tube V3, and since the quenching potential applied to the grid of tube vV4 is less negative than the potential at which'the arc may be started in tube V3, the arc will strike in tube Va. Similarly. upon the opening of switch I3 it will be possible to cause tube V3 to quench. while 'tube V2 has such potentials applied to grid and anode that anarc will strike. The same thing may be accomplished in the case of tube V1 and switch Il, the requirement being .that the quenching potential of each tube should be less negative than the starting potential of the preceding tube in the sequence. In other words, referring -to Fig. 1, each curve Ip represents the operating characteristic of one tube, such as V3. The'curve Ipi must represent the characteristic of the .adjacent tube V2 and the characteristics of each of the pairs of tubes must berelated in the manner shown 'in Fig. l, sothat the quenching potential of the one is less negative than the starting potential of the next. This condition can readily be secured by proper adjustments of anode and grid potentials and by proper choice of tube'and resistances of the anode circuits. The anode and grid pctentials are, of course, determined by the adjustment of resistances R1 to Rs, inclusive, and R11 to R15, inclusive. For the proper quenching operation of the tubes the values of the resistcathode region of the tube. I anode current and results'in arise in potential ances of the windings of relays S1, Sz, Sa and S4 should be properly chosen so that the-total resistance of each individual anode circuit will be of the proper value. That the anode circuit resistance of each of the tubes is a factor entering into the proper quenching operation thereof will be seen from the following. When an arc exists in a tube of the type herein described the critical voltage at which the arc is quenched is determined by two factors: the applied anode potential, and the resistance between such source of anode potential andthe anode terminal of the tube. This results from the factthat when the grid draws positive ions out of the discharge, a negative space charge is built up in the grid-to- This reduces the at the anode. Should the anode voltage and anode resistance bel of such value that this potential rise is suiiicient to overcome the negative grid bias. and restart the discharge, no quench- .ing will occur. However, the anode voltage and anode resistance can in any case be so proportioned that the tube is substantially deionized by the action of the negatively charged grid and proper quenching action obtained.

While the invention has been disclosed as ernbodied in certain specific arrangements which are deemed desirable. it is understood that it is capable of embodiment in many and other widely varied forms without departing from the spirit of the invention as deiined'by the appended claim.

' What is claimed is: lA selective signaling system comprising a setl of gas nlled discharge tubes, said tubes being of the type vwhich have a critical negative grid poltential at which breakdown occurs determined by the potential applied to the anode circuit and a different critical negative grid potential at. which release occurs determined by the potential applied to the anode circuit vtogether with the re- I sistance of .said anode circuit, means for adjusting the potentials applied to the electrodes of said tubes so that one of said tubes will have a fixed anode potential of a sufilciently lower value than that applied to the anode of the preceding tube in the'set whereby said first mentioned tube will discharge and quench with lower values of negative potential applied to the grid thereof than will be needed to start a discharge in the preceding tube of the set, and means for selectively varying the negative potential applied to the grids of said tubes to cause their selective 5s operation.

LYMAN F. MOREHOUSE. SAMUEL P. SHACKLETON. 

